There is a lot of information, research and more for adults on the speaking skill but for our young learners it is hard to find. I have been reading and I guess that by my experience is what I will write about a few ideas.
Children will start speaking English at their own pace, just like the way they speak their mother tongue, some do it so fast that it is amazing, others take more time. I have twins, both would understand and speak Spanish which is our Mother tongue and English came easily for one twin and not for the other. Today, both are fluent in both languages. As for my students I have had the opportunity to see them older and be amazed at how well they can speak English.Even some students that didn't speak a thing in class were very fluent in English.
My advice, keep doing all you can in class for the speaking skill, it will be different for each of your students. They will speak at their own time, be patient. Here are some things that you can do!
1. Use the responsive speaking as your students give short replies to questions.
Teacher: What color is this?
Students: Yellow!!
2. Engage students in speaking activities. Have them name patterns, such as boy, girl, boy, girl.
3. Use short and simple drills. It can be anything. My example: look, a pencil. Look, a book. Look, a chair. Look, a table.
4. Use extensive speaking and prepare show and tell activities. I always include a draw something about the unit worksheet which are perfect for the show and tell. Let me add one here.
5. Use props to aid students into speaking. It can be I like bananas as in the picture. Puppets are useful, too.
6. Promote interaction through pair and group work. I can't say it enough, games are a must for the younger stduents. It makes them speak without knowing! Here is one of the games taht I include in each unit.
7. Use short and simple sentences that you can model for them to repeat at their own pace.
I am sure that you have more ideas to comment below!